Compounds of the class of formula (I) have until now been unknown in the literature; however, the isomerizing cyclization of .alpha.-thiocyanato ketones, which may be improved by acidic or basic catalysis, is known [see e.g. J. Am. Chem. Soc. 74, 1719 (1972); or J. Chem. Soc. 1949, 2898]. According to our knowledge, this reaction type has not been used for the synthesis of .alpha.,.alpha.'-bis derivatives.